Crash when scrolling or watching movie

Since I have installed Windows 7 64bit on my Sony Vaio VGN-FZ31S, my computer sometimes hangs. It stops doing any reactions and I need to force a reboot:

- when i scroll in PDF files (although it works fine most of the time)
- when I view movies in iTunes (computer usually hangs after a couple of minutes). The error does not occur in windows media player

Any advice how I can get to the ground of this issue are much appreciated.

thanks
Nicolas

check eventlogs "eventvwr.msc" check application and system logs check for errors

The systems console says:

A fatal hardware error has occurred.

Reported by component: Processor Core
Error Source: Machine Check Exception
Error Type: Bus/Interconnect Error
Processor ID: 1

The details view of this entry contains further information.

Details:
Source: WHEA-Logger
Event id: 18
level: error
User: LOCAL SERVICE

Memory is fine.... Any other advice?